The invention relates to a method for driving material such as piles or the like into the ground with the aid of a single hammer which is driven by a double-action piston-cylinder unit via a controlled periodically changing stream of pressure medium and which in the driven material induces forces in the longitudinal direction.
The method of driving a pile, a sheet pile or the like into the ground by striking it with the aid of a hammer is known. In this case, the hammer is either raised mechanically and the striking energy is transmitted to the material being driven in by the falling energy of the hammer or, as disclosed in U.S. Pat. No. 2,731,796, the hammer is raised by means of hydraulic oil and is accelerated for the driving stroke in the direction toward the material to be driven in by a hydraulic fluid under pressure, so that in addition to the falling energy of the hammer the actuated pressure energy is converted to striking energy. Such hammer driving is connected with considerable noise development so that additional measures must be taken with respect to noise protection. Moreover, the striking frequency and thus the driving speed is limited.
Recently it has been attempted, instead of striking with a hammer, to vibrate the material into the ground. The vibratory energy is generally generated either by so-called eccentric vibrators or is transmitted to the material to be driven in by hydraulic means with the aid of a pulsating stream of pressure medium. Although vibrating the material has the advantage of considerably less noise development it does have a series of drawbacks. For example, it may happen that after reaching a certain penetration depth for a driven pile, the pile is jammed tight and further penetration of the pile is impossible even with a change in frequency and/or amplitude, although the required penetration depth has not yet been reached. A further drawback of vibrating is that for so-called pile grillage foundations, where proof of load-carrying capability has to be given, this cannot be effected by the driving device, as for example during hammer driving, but that an additional measuring instrument must be provided or the vibratory tool must be exchanged and the last piece of the penetration has to be effected with the aid of a hammer so as to provide the proof of load carrying capability. Exchanging the vibration device for a striking device is also necessary if, as described above, the material being driven in "jams" without having reached the required penetration depth.
The drawbacks of vibrating require either the use of an overdimensioned vibratory device where in a number of cases the proof of load carrying capability must be made with a special testing device or by subsequent hammer driving, or, if a "normally" dimensioned vibratory device is used, a second driving device must be used in any case if the material to be driven in is "jammed", be it a heavier vibratory device or a driving hammer. A further drawback is that upon "jamming" of the material with subsequent shut-off of the energy supply, it requires a substantially greater amount of energy to reinstate the driving process in order to overcome the counteraction of the earth that has settled down in the meantime, so that in addition to the costs for maintaining and assembling a second driving device, there exist, depending on the consistency of the ground, further difficulties with respect to further penetration of the material into the ground.